The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e. cause-and-effect relations, of this interaction. To shed light on the problem, interface-resolved direct numerical simulations of channel flow over a cylinder array for porosity $=0.4$–$0.9$ are performed, and the friction Reynolds number of the top smooth wall is controlled to be $Re_180$. We use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous medium. Correlation analysis and linear coherence spectra are also leveraged to complete the study. Our results show that the permeability of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface–subsurface interactions. The interaction of the free flow and porous medium is further decomposed into two coupling directions, namely, top-down and bottom-up. For low-porosity cases, top-down and bottom-up interactions are strongly asymmetric, the former being mostly influenced by small near-wall eddies, and the latter reflecting the onset of Kelvin–Helmholtz type instabilities due to the perturbation from the porous medium. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.
%0 Journal Article
%1 wang2021information
%A Wang, Wenkang
%A Chu, Xu
%A Lozano-Durán, Adrián
%A Helmig, Rainer
%A Weigand, Bernhard
%B Journal of Fluid Mechanics
%D 2021
%I Cambridge University Press
%K EXC2075 pn1
%P A21--
%R DOI: 10.1017/jfm.2021.445
%T Information transfer between turbulent boundary layers and porous media
%U https://www.cambridge.org/core/article/information-transfer-between-turbulent-boundary-layers-and-porous-media/6791BFCED29848AD37FA3B4D4AA5B684
%V 920
%X The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e. cause-and-effect relations, of this interaction. To shed light on the problem, interface-resolved direct numerical simulations of channel flow over a cylinder array for porosity $=0.4$–$0.9$ are performed, and the friction Reynolds number of the top smooth wall is controlled to be $Re_180$. We use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous medium. Correlation analysis and linear coherence spectra are also leveraged to complete the study. Our results show that the permeability of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface–subsurface interactions. The interaction of the free flow and porous medium is further decomposed into two coupling directions, namely, top-down and bottom-up. For low-porosity cases, top-down and bottom-up interactions are strongly asymmetric, the former being mostly influenced by small near-wall eddies, and the latter reflecting the onset of Kelvin–Helmholtz type instabilities due to the perturbation from the porous medium. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.
@article{wang2021information,
abstract = {The interaction between the flow above and below a permeable wall is a central topic in the study of porous media. While previous investigations have provided compelling evidence of the strong coupling between the two regions, few studies have quantitatively measured the directionality, i.e. cause-and-effect relations, of this interaction. To shed light on the problem, interface-resolved direct numerical simulations of channel flow over a cylinder array for porosity $\varphi =0.4$–$0.9$ are performed, and the friction Reynolds number of the top smooth wall is controlled to be $Re_{\tau }\approx 180$. We use transfer entropy as a marker to evaluate the causal interaction between the free turbulent flow and the porous medium. Correlation analysis and linear coherence spectra are also leveraged to complete the study. Our results show that the permeability of the porous medium has a profound impact on the intensity, time scale and spatial extent of surface–subsurface interactions. The interaction of the free flow and porous medium is further decomposed into two coupling directions, namely, top-down and bottom-up. For low-porosity cases, top-down and bottom-up interactions are strongly asymmetric, the former being mostly influenced by small near-wall eddies, and the latter reflecting the onset of Kelvin–Helmholtz type instabilities due to the perturbation from the porous medium. As the porosity increases, both top-down and bottom-up interactions are dominated by shear-flow instabilities.},
added-at = {2021-10-18T09:26:46.000+0200},
author = {Wang, Wenkang and Chu, Xu and Lozano-Durán, Adrián and Helmig, Rainer and Weigand, Bernhard},
biburl = {https://puma.ub.uni-stuttgart.de/bibtex/26dca48dd70f6bd43d1734e4c50b20ee6/simtechpuma},
booktitle = {Journal of Fluid Mechanics},
doi = {DOI: 10.1017/jfm.2021.445},
interhash = {103e9b75000747cb73f7a0f0392d7b97},
intrahash = {6dca48dd70f6bd43d1734e4c50b20ee6},
issn = {00221120},
keywords = {EXC2075 pn1},
pages = {A21--},
publisher = {Cambridge University Press},
timestamp = {2021-10-18T07:26:46.000+0200},
title = {Information transfer between turbulent boundary layers and porous media},
url = {https://www.cambridge.org/core/article/information-transfer-between-turbulent-boundary-layers-and-porous-media/6791BFCED29848AD37FA3B4D4AA5B684},
volume = 920,
year = 2021
}
